numbers = [1, -2, 3, -4, 5, 6, -7, 8, 9, -10]
list1= []

for i in numbers:
    if i>=0:
        list1.append(i)

# list1 = [ item*2 for item in numbers if item >= 0]

# print(list1)

new_list = [ i for i in list1 if i % 2 == 0]
print(new_list)

# print(list)
# new_list = [i for i in list if i%2==0]
new_list.sort(reverse = True)
print("操作后的列表: ",new_list)
# print("操作前后列表元素总和之差:",sum(numbers)-sum(new_list))